Mechanical stirrer



June 14,193.1 y J, PREgEUTHNER 1,862,906

MECHANICAL STI-RRER a y r 26 Ju//L/.s /Qe/eu/ver JNVENTOR.

ATTORNEY.

June 14,- 1.932. J. PRELl-:UTHNER 1,862,906

MECHANICAL STIRRER Filed Nov. 18, 1950 5 Sheets-Sheet 2 .INVENo/e. u B YA ATTORNEY`- 6 0 nw 2 6 8 l June 14, 1932- J. PREIQEUTHNER MECHANICALSTIRRER 5 Sheets-Sheet Fviled NOV. 18.

' IN VEN TOR. QJ/dum 'A TTORNEY June 14, 1932. l J. PRELEUTHNER1,862,906

MECHANICAL STIRRER Filed Nov. 18, 1950 5 Sheets-Sheet 4 BY gl/) @J/44403A TTORNE Y.

June 14, 1932.

J. PRELEUTHNER MECHANICAL STIRRER Filed Nov. 18, 1930 5 Shset-s`Sheet 5Patented June 14, 1932 UNITED STATES JULIU'S PRELEUTHNER, OF NEW YORK,N. Y.

MECHANICAL STIRRER Application led November 18, 1930. Serial No.496,442.

This invention relates to improvements in mechanical stirrers of theimpeller type, and it is the principal object of my invention to providea device of this character in which two stirrers are connected orcombined to form a unit using a common, upwardly s lanting discharge lipfor the material to be stirred provided with indentations andtooth-shaped projections constituting mixing grids :and

causing frequent changes in the directlons of the discharged currentsand irregular commotions within the aifected batches of the stirredmaterial to promote intimate and eficient mixing. l

Another object of my invention is the provision of a separate suctiontube attached to the bottom of the unit and an intake tube attached tothe top of the unit allowing the bringing together of the independentcharges supplied to the stirrer through said tubes and their dischargeinto a ring-shaped space within the stirrer Where they are impinged uponeach other and intimately and eiiiciently mixed prior to their naldischarge into the main charge being injected at various levels topermit additional mixing with the main charge by virtue ofthe velocityof the various currents created in the stirrer. y

'A further object of my invention is the provision of a mechanical.stirrer of the above character the impeller disk of which is providedWith a plurality of perforations establishing a communication betweenthe channels above and below the impeller to vary the pressures in thecharge and thuseliminating-and reducing axial thrusts in the equipment.l

These and other objects and advantages of -my invention will become morefullyvknown as the description thereof proceeds, and will then bespecifically defined inthe appended claims.

vIn'the accompanying drawings forming a material part of thisdisclosure: l

Fig. 1 is a vertical section through a stirrer constructed according tomy invention on line A--A of Figure 2. y

Fig. 2 is a top plan view of the stirrer, Figure 1.

`further modification of my invention. l

Fig. 3 is an elevation in axial section of a modified form of thestirrer. y

Figa is a view similar to Figure 3 of another modification.

Fig. 5 is an axial section through the form, 55 Figure 4.

Fig. 6 shows a modified form of the stirrer housing.

Fig. 7 is an elevation in axial section of a Fig. 8 is an elevation inaxial section of another modification, the section being taken on lineB-B of Figure 9.

Fig. 9 is a top plan view of the stirrer, Figure 8.

Fig. 10 is an elevation in axial section on line C-C of Figure 11.

Fig. 11 is a top plan View of a still further modified form of stirrer.

Fig. 12 shows in elevation and axial section 70 on line D--D of Figure13 a further modification of my stirrer.

Fig. .13 is a top plan view thereof.

Fig. 14 shows in elevation and axial section another modification of thestirrer.

Fig. 15 is a view similar to Figure 14 of a further modification.

Fig. 16 illustrates in elevation and axial section a stirrer withhorizontal cylindrical tanks. v

5F ig. 17 is an elevation in axial section of another modification ofthe stirrer.

Fig; 18 shows in elevation and axial section a modification of thestirrer having no impeller vanes.

Fig. 19 is a sectional elevation of a modied form of the stirrer, Figure18.

Fig. 20 shows in sectional elevation a still further modiied form ofstirrer.

The drawings are partly diagrammatical. 90 Similar` figures have beenused in the drawings to denote similar parts.-

Reerring now Ato the drawings, primarily toFigs. 1 and 2: the Hat,circular part 1 and the cupped part 2, referred to hereinafter as 95 thetop and bottom, respectively, jointly constitute the housing or casing'3enclosing the lens-shaped, single, undivided cavity 4.

' .The cupped bottom 2 has an upwardly slanting discharge lilr,terminating in the 10 by a plurality of vanes or shrouds 10, originatingWithin the cavity 4 in an imaginary circle 11, for convenience ofreference called the intake circle, and terminating near the outerperiphery of the housing at the aforementioned discharge slot, theiniddleline of which, representing, approximately, the mean eectivedischarge, is called hereinafter, for convenience of reference, thedischarge circle 12.

The vanes are curved so that the hollow or convex surfaces 13 movetowards the charge When the stirrer is rotated, as Will be specifiedlater, the vanes, as it were, shipping or scooping'up the liquid.

The inner terminals 14 of the vanes originate in the aforementionedcircle 11, preferably tangentially or approximately tangentially, so asto offer the 'least resistance at the intake edge 15, which, for thesame reason should be as sharp as possible. Considering the abrasiveeffect of the continuous impact of the charge at this edge, it ispreferable to select for the intake edge angles of from 39 to 60degrees, the drawings showing angles of 60 degrees.

The outer terminals 16 terminatefat the discharge slot 9 in radialdirections, i. e. the terminals intersect the discharge circle 12previously referred to under right angles or approximately right angles.

While the outer terminals thus have fixed positions at, or in proximityof the outer pei riphery, the inner terminals 14 originate at distancesfrom the axis of the stirrer housing which depend upon the properties ofthe charge and upon the rotary speed. For practical and generalpurposes, covering the usual mixtures in chemical processes, also themixtures in oil refining processes, the distance of the intake edge fromthe centre of the stirrer should not be less than one half, or more thanfour-fifths of the radius of the discharge circle previously referredto. If the distance is less than one-half of the discharge circle, theintake, i. e. the scooped up volume is insufficient, the moreinsufficient the nearer the. intake edge is to the centre and the'faster the stirrer is rotated. If the intake edge is further from thecentre than four-fifths of the radius of the discharge circle, theimpact incident -to scooping up material by the vanes is too sudden fora smooth running of the stirrer, causing shocks, vibrations, and as aconsequence, loss of power, quick deterioration and, eventually,breakdowns. In the drawings, the distance previously referred to is,approximately, two-thirds of the radius of the discharge circle.

The most efficient curve for the vanes is the involute, theoretically,but for practical purposes parabolic, circular and other curves of thesecond and fourth order may be adopted. Circular' curves have been shownin the drawings, throughout. Curves of the indicated kind assure acontinuous and constant change of the direction of the flow of theliquid While passing in front of the vanes, thus avoiding shocks andvibrations and the disadvantages incident of the stated irregularitiesof the motion.

Curves designed in accordance with the specified characteristics assurean intake, practically, without resistance, a shockless flow of liquidwhile passing in front of the vanes, receiving continuously andconstantly increasing impulses to a higher velocity, arriving at thedischarge terminals in radial directions where they are hit by themoving vanes at right angles to the direction of the flow, thusreceiving the highest impulse possible under given conditions,discharging, as a consequence, with the highest velocity obtainableunder given conditions.

The stirrer is rigidly mounted upon a rotatable shaft 17 by anyconvenient means, for instance, keys, or, as is indicated in Fig. l, byshrinking the housing upon the shaft, for which purposes a boss 18 isprovided in the centre of the top 1, previously specified.

The stirrer may be actuated by any convenient means, an electric motor,for instance, power being applied either directlyv or by interposedtransmissions which are not indicated in Fig. l, being standardizedparts of the equipment not constituting parts of the invention.

The rotation is determined by the curvature of the vanes, as has beenpointed out hereinbefore, the arrow 19 indicating how the stirrer shouldbe turned with reference to the vanes.

Referring now again to the drawings;

Fig. 3 is a modification in which the top l is domed and the bottom 2 isflat, the stirrer discharging under a downward slant. The suction tube 7is supposed to be attached to the intake 6 by the shrinking method, assuggested at 22. Here, as well, as in the drawings throughout, thedirection of the inflow is indicated by arrows 20 and of the dischargeby arrows 21.

Fig. 4 indicates a modification in which all parts are cast in a unitwith the intake tube 7.

Fig. 5 is a modification indicating a-housing composed of two partsrigidly held together by strips 23 and bolts 24, also shown in a plandetail in Fig. (i.

Fig. 7 indicates a modification in which the cupped bottom part 2 of thehousing and the suction tube 7 are cast as a unit. The manner ofattaching theafore named parts to the tank 27, of which a part of thebottom is only shown, is also indicated by members 25 and bolts 26.A Inthis modification, as well, as in all previously considered forms, theimpeller disk is replaced by the top of the housing. In the present casethe top of the housing, which is provided with a plurality of vanes 10,is rigidly attached to the rotatable shaft 17,

constituting the only operable member of the modification, the bottom ofthe housing, forming in conjunction with the suction tube, what may becalled a suction cup, being stationary.- In this modification the partsconstituting the stirrer are reduced to a possible minimum; so are alsothe movable parts, the top of the housing, or to be more correct, the

impeller being the only movable member.

The power needed to operate the present modification is thus alsoreduced toaJ possible minimum.

Figs. 8 and 9 show the combination of two stirrers in a composite unit,the several pieces, namely the fiat top 1 and the cupped bottom 2constituting, respectively, the top of an upper or first stirrer housingand the bottom of a lower or second stirrer housing, being rigidlyattached to each other and also to cross beams atop the tank by hangers28, members 29 and bolts 30 and 31. The details of.at taching theaforementioned hangers to crossbeams on top of the tank are not shown inthe drawings being known members of tank equipment not constitutingparts ofthis invention. The members 29 and 31 are also omitted in Fig.9.

Between the afore specified parts l and 2' is the shaft mounted.rotatable impeller comprising the impeller disk 32, which in the presentinstance, constitutes, respectively, the bottom and the top of the aforementioned first and second stirrer housing. The impeller disk isprovided with a plurality of vanes 10. All members of this modification,as previously referred to, constitute two stirrers combined in a singleunit, each of these two stirrers conforming in most details to themodification shown in Fig. 7. or in a wider sense to the stirrer shownin Figs. l and 2.

In studying the modification disclosed in Figs. 8 and 9, it may beobserved that both, combined stirrers utilize a common, upwardlyslanting discharge lip 5 which is a part of the cupped bottom 2, the lipprojecting above the level of the discharge which, in the present formis the upper edge 35 of the vanes 10. Impeller type stirrers of knowndesign in which two stirrer units are combined use for each stirrer unita separate discharge lip. The advantage of a common, slanting dischargelip has been previously pointed out.

The lip 5, in this modification is provided with indentations 36 andteethshaped proing grids. Such grids formed by irregularities in thecontinuity of the discharge lips or rims, elther of the cupped or of theflat or of both parts constituting the housing may be incorporated inthelstirrers by manufacturing t e stirrers accordingly, or they-may beattached as separate members as will be specified later and as shown inFigs. 10 and 11.

The modification indicates also a separate suction tube 7 attached tothe bottom of the unit by bolts 8, and a suction or intake -tube 42attached 'to the top of the stirrer unit by bolts 43, both tubessuggesting the intake of portions of the charge by suction from the topand the bottom levels, respectively, also the addition of materialduring operation directly into the cavity of the stirrer trough theafore specified tube 4t2.l The affected portions of the charge drawnfrom widely distant parts of the tank or added independently are broughttogether within the cavities of the two combined stirrer units beingdischarged primarily into the ring shaped space 89 within the stirrerhousing where they are impinged upon each other and intimately andefficiently mixed prior to their final discharge into the main charge,being injected here into various levels promoting additional mixingwithin the main charge by virtueof the velocity of the currents.

Attention is called here to the particular novel design of combinationsin a single operative unit of two impeller type stirrers. Combinationsof this type incorporating two stirrers in a unit, but usually specifiedas a single stirrer are known. They have in common with the presentmodification a housing comprising a top and a bottom part and animpeller intermediate of the aforementioned two parts of the housing,the impeller comprising a circular disk and, integral thereof, aplurality of vanes. In designs known heretofore, each of the stirrersincorporated in the combination use a separate discharge lip while thepresent design utilizes for both discharges a common, slanting dischargelip as has been pointed out before. Additionally, in stirrers of knowndesign the vanes terminate in close proximity of the periphery of thehousing, while in the present modification the vanes terminate somewhatshort of the inner surface of the housing in proximity of the dischargelip, thus leaving a ringshaped space, the aforementioned mixing chamber89, wherein the respective discharges from the upper and the lowerstirrer are impinged upon each other with unreduced velocity, prior totheir final discharge into the main charge. In stirrcrs of known design,having vanes terminating at the discharge opening the discharge isdirect into the main charge and although the affected portions are mixedwith each other and also with the main charge at the discharge openingbut outside of the cavity the mixing is considerably less intimate thanin the prescnt forms in which first mixing of the diS- charged portionsis effected and subsequently the mixing of this mixture with the charge,in the process tank.

This modification indicates also a method of attaching a shaft composedof a steel core 17 and a protecting cover of lead 38, attached,preferably homogeneously, to the core by any convenient method, to thestirrer, in a manner assuring protection of the steel core from contactwith corrosive charges, as, for instance, used in oil refiningprocesses. For this purpose, the steel core is exposed at the lo .'erterminal by removing therefrom the lead, and after the steel core issecured in the stirrer body by any suitable method, for instance, by akey 39, the'recess at the lower surface of the impeller disk and theringshaped gap above the impeller disk are filled with lead by theso-called lead burning process, as is indicated at 40 and 41 in Fig. 8.

The modification shows also perforations in the impeller disk, theseperforations 90 establishingT a communication between the chambers aboveand below the impeller, contributing the occasionally differentpressures in the affected portions of the charge, thus eliminating orreducing axial thrusts in the equipment.

In Fig. 9 the relative paths of portions of the liquid while passingfrom central to peripheral sections within the cavity 4 of the stirrerare indicated by arrows 33 and 34. The arrows 33 suggest the path withreference to the vanes, relatively, the stirrer assumed not to rotate,the particles, however, moving as if the stirrer were in rotation. Thearrows 34 show, approximately the actual path, the stirrer supposed torotate.

Attention is here called to the omission in Fig. 9 of the parts 29, 31,38, 39, and 42, for simplicity.

Figs. 10 and 11 indicate a modification resembling the one shown inFigs. 8 and 9, all

parts, however, being cast in a single unit.

The modification incorporates also a separate mixing grid 44 providedwith indentatioiis 36 and teethshaped projections 37 along thecircumference, and the manner of attaching this grid to the top 1 of thehousing by bolts 45. The impeller disk 32 shows also pressure equalizingperforations 90.

Figs. 12 and 13 indicate in operable relation the combination of; astationary suction tube 7 attached by members 46 and 47 to the conebottom 4'8 of the tank 27, a part of the bottom being shown only, acupped bottom 2 of the housing rigidly attached to the tank by thepartly shown members 49, a rotatable stirrer unit comprising .the top 1and cast therewith ina unit an impeller comprising a perforated im ellerdisk 32 and a plurality of double acting vanes 10, a stationary tube 42provided with a branch tube 50 wherethrough material may be added intothe cavity of the stirrer, as indicated by the arrows 5l, a shaft 17projecting downwardly into the tube 7 and a bearing 52 secured in thetube 7 by braces 53 and bolts or rivets 54, the bearing indicating amethod of steadying the impeller shaft in the suction tube 7. Theupwardly projecting lip 5 of the stationary, cupped part 2 is providedwith indentations 36 and teethshaped projections 37, and a small,ringshaped mixing chamber 89 is indicated in proximity of the slantingdischarge lip 5. In operation, the actions of the double vanes of theimpeller cause portions of the charge to enter the chambers below andabove the impeller, forcing them into the mixing chamber 89 where theyare impinged upon each other and finally discharged into the maincharge, similar, as has been specified previously, with reference toother modifications. f

Fig. 14 indicates the use of a stirrer unit in the top levels of acharge and the manner how material may be pumped into the cavity of thestirrer from the bottom levels through a stationary suction tube 7attached by members 46 and 47 to the cone bottom 48 and by members 55and 56 to the cylindrical shelly of the vertical tank 27, a circularplate rigidly attached to the upper terminal of this tube 7 constitutingthe stationary flat bottom 2 of the stirrer equipment. The cupped or domed member 2 provided on the convex inside with a plurality of vanes10, and rigidly attached to the rotatable shaft 17, said member 2constituting-in this case the rotatable top of the impeller housing, ismounted coaxially and in operable relation to the said tub-e 7, themethodof deriving power being indicated, diagrammatically, by bevelgears and pulleys 76, 77 and 78, operably mounted upon the crossbeam 60on to of the tank.

In operation, material Willpbe pumped, primarily, from the low levels ofthe charge through the suction tube 7 into the cavity of the stirrer andfinally ejected therefrom in a slanting direction into the top stratasof the charge, the downwardly slanting, either continuous or irregulardischarge lip 5 causing the discharged batches to be expelled indiagonal directions, as indicated by the arrows 21. Considerable heightsmay be negotiated, the counterpressure of the liquid in the tankassisting and facilitating the lift. ,Fig 15 indicates an equipmentcomprissecured in the impeller disk,

ingFa unit resembling the modification shown in igs. 12 and 13 namely, astirrer unit 57 provided with a downwardly slantin discharge lip 5,operably mounted upon t e rotatable shaft 17, in combination with anintake tube 59 attached to the crossbeam 60 on top of the tank 27 bybraces 61 and bolts 62, a supply tube 63 controlled by a valve 64 and ahand-wheel 65 connecting a supply tank 66, rigidly mounted upon theaforespecified crossbeams 60, with the intake tube 59 previouslyspecified. This equipment is in co-axial disposition with the lower partof the housing formed by the cupped bottom 2 provided with a suctiontube 7 and stationary attached to the bottom 48 of the tank 27.

In operation, portions of the charge entering the stirrer through thetubes 7 and 59 are mixed within the housing and finally discharged intothe main charge in directions indicated by the arrows 21.

Fig. 16 indicates a cylindrical tank 67 placed with the axishorizontally, in combination with a horizontally discharging stirrer 68mounted upon a horizontal shaft 17. The shaft is supported in a knownmanner, by the brackets 69 of which only one 1s shown and power isderived through pulleys 70. A bent tube 7 attached to the tank 67 bybrackets 71 and bolts 72, terminating 1n operable relation to thestirrer 68 indicates how material may be sucked into the stirrer fromthe lower levels of the charge.

Fig. 17 indicates the co-operative use of two stirrers or impellersrotating in opposite directions, namely, the stirrer 57 rigidly mountedupon the hollow shaft 73, and the impeller 58 rigidly mounted upon thesolid shaft 17 which is co-axially disposed to and within the hollowshaft 73. The shafts may be driven in opposite directions byv a systemof bevel gears and pulleys 74, 75, 76, 77, 7 8 and 79 which areadequately mounted upon the top of the tank. Each pair of bevel gears isassigned to drive one of the shafts, the

gears 74 and 75, for instance, the hollow shaft- 7 3, the gears beingsuitably secured to their respective shafts, or instance, by keys.

This modification indicates also a method of steadying the stirrershafts without the use of the usual bearing brackets which arepreferably avoided in the present case, in view of the comparativelyconsiderable height required. The solid shaft 17 rigidly secured in thebevel gear 76 and in the impeller 58 is supported in a bearing 8(conveniently attached in a manner not shown in the drawings to thepartly shown cone bottom 48 of the partly shown tank 27 preferablyprovided with an exchangeable wearing plate 81 of suitable material, andalso in a bearing 82 secured within the hollow shaft 73 in anyconvenient manner, so as not to obstruct entirely the clear opening ofsaid hollow shaft. The hollow shaft 73 is steadied against transversemotions by the antifriction ball race 84, the shaft being rotatablyadmitted in the central bore ofthe afore mentioned ball race 84 andtheball race being secured against side motions by the vertical sde of thecircular race pan 85 conveniently attached to the top beams 60 of thetank, details of this attachment omitted in the drawings. This hollowshaft 73 is also secured against vertical motions, partly by its ownweight and partly by the bevel gear to which it is rigidly attached aspreviously stated, said gear being held in position, considering anupward motion, by the bevel 74 previously referred to.

'lhe drawings show also a stationary intake tube 59 attached in asuitable manner to the top beams 60 across the tank 27 having a similarobject as the tube 59 specified with reference to the modification shownin Fig. 15, namely, the adding of material during operation, eithercontinuously or intermittently, through this tube directly into thecavity vof the stirrer, so as to save time and power otherwisenecessary. The tube 59 is provided with a branch tube 50 wherethroughmaterial may'be added as suggested by the arrows 51 and in addition tosuch material as added through said tubes from the ou'tside, portions ofthe charge may enter the tube 59 through apertures 87.

Here, as well as in previously specified modifications, the upwardlyslanting discharge lip 5, projecting above the discharge level of thecombined stirrers 57 and 58 is an outstanding feature assuring ecientmixing. This lip is in the presently discussed modification providedwith irregularities, the indentations 36 and the teethshaped projections37 which contribute to the promotion of numerous irregular currents, inproximity of the discharge from the stirrer.

This modification permits the disposition of the rotatable parts of theequipment in any level of the charge, assuring as well a supply ofmaterial within the stirrer from the outside, as from the bottom strataand from the top strat-a of the charge. Material may be added from theoutside also through the small tubes 86 and 88, diagrammaticallyindicated in the drawings, operably terminating at the upper terminalsof the intake tube 59 and the hollow shaft 7 3, respectively.

In operation, material entering the stirrer as suggested previously,being either charged from the outside, or drawn into the cavity of estirrer equipment from the bottom and top strata of the main charge, ismixed, primarily, within the cavity of the stirrer, subsequentlydischarged with impinging force into the aforespecified mixing chamber89, wherein intimate mixing takes place, whereupon the mixed batches aredischarged and forcibly injected into the main charge where additionalmixing is accomplished, not

onl in the neighborhood of the discharge an in the level of the stirrerbut, in consideration of the slanting and irregular currents, in alllevels and distant portions of the tank.

Considering also that the impellers of the equipment rotate in oppositedirections, the portions are impinged upon each other withm the mixingchamber in opposite d1rect1ons, utilizing the velocities imparted tothem by the vanes of the stirrer exclusively for mixing, discharge beinaccomplished by the radial components on the discharge currentstherefore having ra ial directions, not, as 1n stirrers of known design,tangential directions, the latter currents causing Within the maincharge an inefficient rotation of the charge in concentric currents.

Fig. 18 indicates a, modilication without vanes, cro-rotation of theliquid within the cavity of the stirrer with the stirrer being promotedby frictional impulses. Stirrers of this type may be advantageouslyutilized for the production of emulsions. They have to be rotated athigher speeds than stlrrers for mixing purposes and in consideration ofthe higher speeds required the stirrers have to be balanced morecarefully than others. Balancing comprises the tests and the correctionsof the stirrers with regard tp an accurate mass distribution around theaxis. Balancing ma be accomplished easier and with greater egrees ofabsolute concentricity if the stirrers are cast without vanes.

Fig. 19 indicates a similar modification having no actual vanes, thecupped bottom 2 provided with a continuous slanting lip 5 projectingabove the discharge level which in the present instance is the level ofthe flat, rotatable top 1, however, is rigidly attached to the partlyshown bottom 48 of the process tank by members 25 and bolts 26.

In operation, the rotating top 1 replacing the impeller, causes theco-rotation of the portions of the char e entrained within the cavity ofthe stirrer housing, discharging the affected portions by virtue of thecentrifugal force developed, discharge being accomplished through theringsha ed discharge slot 9 in directions suggested the arrows 21,replacement of the dlssipate volumes being accomplished by suction fromthe main charge into the stirrer through the intake opening 6 indirections indicated by arrows'20.

Fig. 20 indicates a modiiication utilizing nozzles or tuyres screwed inthe housing or secured in other suitable manner, the nozzles beingdisposed at the outer periphery of the stirrer, replacing theaforespecified discharge slot 9. The modification shows also a piece ofpiping used as a suction tube 7 this member being stationary andyrigidly attached to the partly shown bottom 48 of a I tank by bracesand bolts 25 and 26.

Nozzles are advantageously utilized for the production of emulsions, thematerial being discharged from the stirrer into the main charge in line,impinging streams, in a manner similar to the one specified previously.

While the invention has been illustrated in its basic form and inmodifications and-va rious applications in what are consideredpreferable forms, it is pointed out that the examples shown may beadditionally variously modified without departing from the spirit of theinvention which is not limited to the structures disclosed and which ismaintained as long as the novel features shown in the most primitiveform in Figs. 1 andy 2 and in more elaborate forms in otherillustrations accompanying this specification are incorporated. Theseimprovements may be summ'arized as follows:

stirrer comprising a rotatably shaftmounted housing enclosing a vaned orvaneless, single, undivided, lensshaped cavity, the lensshaped housingcomposed of a flat and a domed part, a central intake aperture in one ofthe two parts constituting the housing one of the two parts of thehousing replacing the impeller disk, the domed part of the housingprovided with a continuous or irregular slanting discharge lipterminating either in or beyond the level of the discharge, the flatpart of the housing provided with a continuous or irregular, circularrim, pressure equalizing holes in the imp eller disk or in the impellerdisk replacing element, vanes of a special curvature, stationary orco-rotating suction tubes disposed below or superimposing the stirrerhousing, the use of said suction tubes as means for charging materialdirectly into the cavity of the stirrer, the cooperatlve use of twostirrers in close proximity of each other, the use of two stirrers inclose proximit of each other, so as to rotate in opposite irections, theuse of hollow shafting for the transmission of power in stirrerequipment, the use of hollow shafts for charging material therethrough'into the cavity of the stirrer housing, the use of bearings withinmembers of the equipment for the support of the shaft, the use ofhorizontally discharging stirrers, the use of bent and inclined suctiontubes, the use of a part of the housing as a common discharging elementfor two or more stirrers in combination, the provision of an internalmixing chamber within said common dischar ng element wherein the batchesdischarged fgrlom two'stirrers operating in close proximity of eachother are mixed prior to their discharge into the main tank, the mannerof supporting shafts and hollow shafts without the use of bearingbrackets, finally the use of discharge nozzles.

Having thus described my invention what claim as new and desire tosecure by Letters Patent is: A

1. A mechanical stirrer comprising two iic stirrer units, a housing forone unit, a dat top for said housing, constituting an impeller disc, anda cup-shaped element, said Hat disc and said cup-shaped partconstituting the housing for the second unit, a means` for rotating saiddisc, a common upwardly slanting discharge lip forming part of saidcupshaped element provided with a plurality of indentations for causingfrequent changes in the direction of the discharge currents andirregular commotions therein to promote intimate and eicient mixing,means for uniting the units, and separate inlet or suction tubes foreach unit. 2. A mechanical stirrer comprising two integrally formedstirrer units, the bottom part of one and the top of the other unitformed by a rotary implement constituting an impeller, a cup-shapedmember forming with said impeller one unit housing, a slanting dischargelip on said member projecting above the level of the discharge, commonto both stirrer units, said impeller having a plurality of pressureequalizing openings, irregular elements formed on the rim of said disc,a

ring-shaped mixing chamber within said cupshaped member, and separateinlet tubes for said units.

3. A mechanical stirrer comprising two integra-l stirrer units acup-shaped bottom member for one unit having an upwardly slantingdischarge lip common to both units, the bottom of one unit and the topof the other unit formed by an impeller disc having pressure equalizingopenings formed therein, a mixing grid attached to the top unit providedwith a plurality of teeth forming indentations, and an inlet tube formedwith each unit.

Signed at New York, in the county of New York, and State of New York,this 28th day of October, A, D. 1930.

JULIUS PRELEUTHN ER.

